1. Field of the Invention
The present invention relates to a zoom lens system, and more particularly, to an inner zoom lens system for use in an image-pickup camera module having an image sensor and which is appropriate for an inner-focus type.
2. Description of the Related Art
In a focusing system of a zoom lens, a front-focus type for moving a first lens group closest to an object side is generally used.
Since in the front-focus type a movement amount of the first lens group required for focusing an object positioned at the same distance does not depend on a focal length, the front-focus type is widely used.
However, since the front-focus type moves the first lens group which is relatively big and heavy to perform focusing, the front-focus type has a disadvantage that a focusing speed is slow in performing auto-focus.
Further, a plurality of lenses are generally used to obtain excellent optical characteristics such as a high resolution, thus a camera module gets big in its size and difficult to mount on a portable apparatus. Still further, since the first lens group is moved to the outside when zooming is performed, the front-focus type has a problem in applying to a portable apparatus.
Another further, since the first lens group is moved to the outside, use of the front-focus type cannot be properly applied to the cases where there is limitation in moving a lens to the outside such as a mobile phone or an outside space is limited.
In the meantime, for another focusing system of a zoom lens, there is a rear-focus type for moving a lens of an image plane side.
The rear-focus type has a problem that a movement amount of a focusing lens required for focusing an object positioned at the same distance is varied depending on a zooming position and that a focus is lost when zooming is performed after a close distant object is once focused.
To improve such problems, a zoom lens system which uses a small combination of lenses and can be manufactured in a small size while realizing a high resolution and a sufficient zooming performance, is required.